RO water has to stored in plastic be because it is acidic. Most people don't realize that after you RO filter your water you need to add alkalinity back to it. Also if you get the ppm too low, it will leach nutrients from your body when you drink it. It's not healthy to RO/ deionize water then just drink it without adding some CaCO3 to bring the ppm and pH back to a reasonable level. Some multistage filters do this to some extent, but it really needs to be tested to confirm the levels are acceptable and that the filter system is working as expected. The brief interaction with a polypropylene liner is not a problem at all at room temperature though.